It is well known to aerate wastewater by injecting air under pressure into the water. The air is mixed with the wastewater and injected as a horizontal jet plume containing a multiplicity of bubbles for excellent water/air contact. This plume rises as a vertical jet flux that maximizes the contact and thereby overcomes as much as possible the low solubility of oxygen and consequent low rate of oxygen transfer between the air and the water. This is done to oxidize and kill many biologically active and potentially harmful bacteria. Such systems are described in French Pat. No. 1,377,571 filed Sept. 27, 1963 by Establissements Luchaire and in U.S. Pat. No. 3,984,323 of F. Evens as well as in Wastewater Engineering: Treatment, Disposal, Reuse by Metcalf and Eddy, Inc. (McGraw-Hill: 1979).
In order to maximize the contact time and thereby concomitantly increase the oxygen absorption it has been suggested to form the horizontal jet plume inside a horizontally elongated underwater tube. This tube is formed of a screen and is provided over at least its upper portion with a cap so that bubbles that pass upwardly through the screen are captured under the cap. Such an arrangement maintains the bubbles as small as possible so that the surface area exposed to the water is as large as possible.
Such devices frequently become clogged, as the water intake for the jet pump pulls in some particulate material that fouls the screen and makes it gas impervious. The entire device normally stands on the bottom of the body of water being treated and generates considerable turbulence, so that the water around the water intake is more laden with particles than the rest of the wastewater. Furthermore it is frequently necessary to protect the compressor needed for such a pump from changes in water level by providing it on land next to the body of wastewater being treated. This requires long hoses and leaves the compressor in a location where it could come to harm from human hands and where the considerable noise it generates can bother persons living or working nearby.